Greg (version 2.0.2)

bread.ols: Getting the bread for the vcovHC

Description

The original bread.lm uses the summary.lm function it seems like a quick fix and I've therefore created the original bread definition: $(X'X)^-1$

Usage

# S3 method for ols
bread(x, ...)

Value

matrix The bread for the sandwich vcovHC function

Arguments

x

The ols model fit

...

arguments passed to methods.

Examples

# Generate some data
n <- 500
x1 <- runif(n) * 2
x2 <- runif(n)
y <- x1^3 + x2 + rnorm(n)

library(rms)
library(sandwich)
dd <- datadist(x1, x2, y)
org.op <- options(datadist = "dd")

# Main function
f <- ols(y ~ rcs(x1, 3) + x2)

# Check the bread
bread(f)
# Check the HC-matrix
vcovHC(f, type = "HC4m")
# Adjust the model so that it uses the HC4m variance
f_rob <- robcov_alt(f, type = "HC4m")
# Get the new HC4m-matrix
# - this function just returns the f_rob$var matrix
vcov(f_rob)
# Now check the confidence interval for the function
confint(f_rob)

options(org.op)